Many businesses utilize mainframe or minicomputers such as IBM mainframes, the Hewlett Packard HP3000, the IBM AS/400, and Digital Equipment Corporation VAX computers to maintain and manipulate essential information, such as accounting data. At one time, access to the programs, and therefore the data, was available only through dedicated terminals, which were connected directly to the computer or to a network on which the computers resided. However, as the use of personal computers in businesses became widespread, terminal emulation programs were developed that ran on personal computers. A terminal emulation program allows a personal computer (PC) to function as a terminal to a host mainframe or minicomputer. The PC monitor displays the information that a dedicated host terminal would display, while alphanumeric data entered with the PC is passed to the host computer in the same manner as if the data were entered with a dedicated terminal.
IBM has developed a library of application programmer interface (API) functions known as Emulator High-Level Language Application Programmer Interface (EHLLAPI), for communicating between an application running on a PC and a host application running on a mainframe or minicomputer. EHLLAPI allows programmers to develop PC applications that function as terminal emulators, thereby allowing an operator to interact with the host application program by entering commands at a PC keyboard. EHLLAPI has served as the industry-wide standard API for communicating between a host computer and a PC. Windows HLLAPI was created by a consortium of leading software manufacturers to serve as a standard EHLAPPI-style API for the Microsoft Windows.RTM. environment.
The RUMBA.RTM. connectivity software, developed by Wall Data Incorporated, is a computer program that also runs in the Microsoft Windows environment. A RUMBA program establishes a communications link with a host computer. RUMBA connectivity software allows the user of a PC to connect to a host computer in order to view stored data and to add new data. RUMBA provides a window on the PC within which an operator can access and manipulate data from a host computer. The communications link and window are referred to as a RUMBA session. The host computer creates a memory buffer containing data that is displayed on the host terminal, if such a terminal is used. The visual representation of the host memory buffer, referred to as a presentation space, is displayed within a RUMBA window, allowing an operator to manipulate the window utilizing standard Windows techniques, such as resizing or moving the window. RUMBA also provides software and an API known as RUMBA Tools For HLLAPI-WinHLLAPI which allows a Windows application to communicate with a RUMBA session. Using the RUMBA tools, a Windows application may request services from the RUMBA session, such as requesting a string displayed within the RUMBA session, or send keystrokes, commands, and strings to the host application.
A host application contains many different types of information screens, each screen including one or more fields. A field can be text or numeric information. The screens may change as a result of a request from the Windows application, forwarded by RUMBA to the host, or as a result of other events, such as an error. When a screen changes, the identity of the new screen cannot always be predicted by the Windows application. In order for an application program to communicate with the host, however, the application program must be able to correctly identify each new screen presented by the host computer. Having knowledge of the current screen, an application program can be structured to understand what each field of information contains. A method for identifying screens presented by a host computer application would assist in the development of a Windows application.
Some host computers, in particular IBM mainframes and AS/400 computers, have field-formatted screens. In a field-formatted screen, each field has a corresponding field attributes descriptor that identifies particular characteristics of the associated field. The field attributes descriptor contains information such as whether the field is protected or unprotected, the type of data (i.e., string or numeric) contained within the field, as well as other information. When an application program requests a data stream containing the data corresponding to a presentation space, each field attributes descriptor is included in the data stream immediately prior to its associated field. The application program accesses a field attributes descriptor by using a function call specifying the X, Y coordinates, in character units of the field within the host screen. In response to such a function call, the RUMBA Tools for HLLAPI-WinHLLAPI returns a binary word wherein each bit of the code word signifies a particular characteristic of the field. Using conventional programming techniques, a program must extract the particular bit for the field characteristic it is interested in. Although this technique of accessing field attributes descriptors and fields has been used extensively, an improved and simplified method of accessing fields and field attributes descriptors is desired.
Despite the successful use of EHLLAPI and its progeny, a need exists for improved methods and techniques of accessing and interacting with data residing on a host computer, in order to reduce the complexity and time of developing and maintaining application programs that are designed to interface with a remotely located computer.